Myoelectric brace

ABSTRACT

A myoelectric brace consisting of a fixed wrist-hand splint portion having a movable finger support portion pivotally secured thereto which is operated by a hydraulic actuator. The actuator is hydraulically coupled to a pump which is driven by a battery powered, direct current motor. Three skin electrodes are positioned on the patient&#39;&#39;s arm and sense muscle potentials in the patient&#39;&#39;s arm when the patient tenses a muscle in the immediate area of the skin electrodes. The resulting myopotentials are then amplified by a muscle potential amplifier and are transformed into a slowly varying control signal by a detector circuit and a filter circuit. The control signal enters a differential amplifier where it causes the motor to drive the hydraulic pump until a predetermined pressure is reached. Actuation of the hydraulic pump causes the hydraulic actuator to pivotally move the finger support towards the fixed splint portion. The motor stops when the differential amplifier receives a signal from the pressure transducer equal in amplitude to the control signal. This causes the differential amplifier output signal to go to zero. Relaxation of the patient&#39;&#39;s muscle causes the finger support to pivotally move away from the fixed splint portion.

United States Patent [72] Inventor Allan G. Potter Ames, Iowa [21] Appl.No. 848,919

[22] Filed Aug. 11, 1969 [45] Patented Jan. 4, 1972 [73] Assignee IowaState University Research Foundation Ames, Iowa [54] MYOELECTRIC BRACEMyo-Electric Control of Powered Prostheses by A. H. Bottomley, TheJournal of Bone & Joint Surgery, Vol. 47B,No.3,Aug.1965,pp.411-415,3-1.1

Gas-Powered Sources and Actuators for Prosthetic and Orthotic Devices"by J. R. Pearson, The Control of External Power in Upper-ExtremityRehabilitation, Nat. Academy of Sciences- Nat. Research Council, Wash.,DC, 1966, pp. 196-197 (FIG. 5) copy in P.O. Scientific Library (RD756-N32C). 3-1.2

Myoelectric Control Systems" by W. Waring et al.,

Orthopedic & Prosthetic Appl. Journal, Vol. 21, No. 1, Mar. 1967, pp.27-32. 3l.l

Myo-Electrically Controlled Electric Torque Motor for the Flexor HingeHand Splint by C. 'Irombley et al., Orthopedic & Prosthetic ApplianceJournal, Vol. 21, No. 1, Mar. 1967, pp. 39-43. 3-1.1

Primary ExaminerRichard A. Gaudet Assistant Examiner-Ronald L. F rinksAttorney-Zarley, McKee & Thomte ABSTRACT: A myoelectric brace consistingof a fixed wristband splint portion having a movable finger supportportion pivotally secured thereto which is operated by a hydraulicactuator. The actuator is hydraulically coupled to a pump which isdriven by a battery powered, direct current motor. Three skin electrodesare positioned on the patients arm and sense muscle potentials in thepatients arm when the patient tenses a muscle in the immediate area ofthe skin electrodes. The resulting myo-potentials are then amplified bya muscle potential amplifier and are transformed into a slowly varyingcontrol signal by a detector circuit and a filter circuit. The controlsignal enters a differential amplifier where it causes the motor todrive the hydraulic pump until a predetermined pressure is reached.Actuation of the hydraulic pump causes the hydraulic actuator topivotally move the finger support towards the fixed splint portion. Themotor stops when the differential amplifier receives a signal from thepressure transducer equal in amplitude to the control signal. Thiscauses the differential amplifier output signal to go to zero.Relaxation of the patients muscle causes the finger support to pivotallymove away from the fixed splint portion.

PATENTEDJAN 41912 3531.542

SHEET 1 [IF 2 Arrow/945 MYOELECTRIC BRACE Electrically powered orthoticdevices or braces for quadraplegic patients are convenient because theelectrical power is readily available and is easily stored in thebatteries which drive the electric motors on wheel chairs used by suchpatients. The utilization of other types of energy storage techniques bythese patients requires the handling of another source of energy andthus, another set of operating conditions which is highly undesirable.In order to utilize the electrical energy stored in the wheel chairbatteries to effectively power orthotic devices, one must optimizeseveral conflicting requirements. First, both the weight and size of thebracemounted actuator must be small. Second, the response and control ofthe limb brace when driven by the actuator must be normal. Third,minimum size, weight, and power consumption is desired for the completedevice.

Therefore, it is a principal object of this invention to pro vide amyoelectric brace for quadraplegic patients.

A further object of this invention is to provide a myoelectric bracewhich is powered by a unique hydraulic system driven by a direct currentbattery operated motor.

A further object of this invention is to provide a myoelectric bracewhich is light weight.

A further object of this invention is to provide a myoelectric bracewhich has a minimum size and consumes a minimum of power.

A further object of this invention is to provide a myoelectric bracewhich is operated by the muscle potentials in the patients arm.

A further object of this invention is to provide a myoelectric bracewherein muscle potentials are sensed by surface electrodes and are usedto control finger position and tension in a proportional manner.

A further object of this invention is to provide a method of actuating amyoelectric brace.

A further object of this invention is to provide a myoelectric bracewhich is economical of manufacture, durable in use and refined inappearance.

These and other objects will be apparent to those skilled in the art.

This invention consists in the construction, arrangements, andcombination of the various parts of the device, whereby the objectscontemplated are attained as hereinafter more fully set forth,specifically pointed out in the claims, and illustrated in theaccompanying drawings in which:

FIG. I is a side elevational view of the brace mounted on the patientsarm;

FIG. 2 is a top view of the brace as seen along lines 22 of FIG. I;

FIG. 3 is a longitudinal sectional view of the hydraulic actuator asseen along lines 3-3 of FIG. 1;

FIG. 4 is a fragmentary longitudinal sectional view of the hydraulicpump as seen along lines 4-4 of FIG. 1;

FIG. 5 is a block diagram of the electrical circuitry of this invention;and

FIG. 6 is a schematic view of the electrical circuitry of thisinvention.

The numeral 10 generally designates a fixed wrist-hand splint of thisinvention which is adapted to be secured to the patients lower arm,wrist and hand. Splint 10 includes a splint portion 12 which is securedto the patients arm 14 by a strap 16 extending therearound andselectively closed by a Velcro fastener means 18 (FIG. I). The upper endof splint portion 20 is pivotally connected to the lower end of splintportion 12 by a pin 22. Thumb support 24 extends downwardly from one endof splint portion 20 and is adapted to have the patient's thumb receivedtherein (FIG. I). A curved support 26 is pivotally secured at its upperend to splint portion 20 by a pin 28 and has spaced-apart, fingersupports 30 and 32 extending laterally therefrom. As seen in FIG. I,finger support 30 is adapted to have the patients fingers extendingtherethrough while finger support 32 is adapted to extend over thepatient's fingers. An arcuate hand support 34 is secured to splintportion 20 and extends laterally therefrom adapted to cup or support theunderside of the patients hand. Strap 36 extends around the patientshand to firmly maintain the device thereon.

A hydraulic actuator 38 is secured to splint portion 20 by bracket 40and has a push rod 42 slidably extending therefrom which is pivotallysecured by a pin 44 to one ofthe adjustment holes 46 formed in ear 48which extends from the rearward end of support 26. Thus, extension ofpush rod 42 from the hydraulic actuator 38 causes support 26 to pivottowards thumb support 24. Conversely, the withdrawal of push rod 42 intothe actuator 38 causes support 26 to pivot away from the thumb support24.

Hydraulic actuator 38 includes a piston head portion 50 secured tocylinder housing 52 by head screws 54. A bellowfram 56 is positionedbetween piston head portion SI) and cylinder housing 52 as seen in FIG.3. A U-shaped piston 58 is secured to bellowfram 56 by a piston capscrew 60 extending through piston cap 62, bellowfram 56 and into piston58.

Push rod 42 is secured to piston 58 and extends through spaced apartball bushings 64 and 66 to reduce friction. A helical compression spring68 embraces push rod 42 between piston 58 and support 70 and yieldablyresists the extension of push rod 42 from housing 52. Nipple 72 extendsfrom piston head portion 50 and is adapted to have a fluid line 74connected thereto to place the fluid chamber 76 in actuator 38 incommunication with pump 78. Pump 78 includes a hollow piston head 80having a nipple 82 extending therefrom adapted to receive the fluid line74 thereon. Pump 78 includes a fluid chamber 84 having a pressuretransducer 86 extending thereinto. Pressure transducer 86 is providedwith an electrical lead 88 which extends to a differential amplifierwhich will be discussed hereinafter.

A bellowfram 90 is positioned between piston head 80 and cylinderhousing 92 by means of cap screws 94. A U-shaped piston 96 is secured tothe center of bellowfram 90 by cap screws 98 extending through cap 100,bellowfram 90 and into piston 96.

The other end of piston 96 has an end plate 104 secured thereto whichbears against the ball bearing screw nut I02 which runs in a groove of agrooved helical screw I16. Screw 116 is secured to the drive shaft I05which rotatably extends from a battery operated, direct current motor106. The numeral 108 refers to a coupling housing positioned betweenmotor I06 and housing 92 and maintained therebetween by screws 110. Anoldham coupling 120 connects motor 106 to screw 116.

Energization of the motor 106 causes power shaft to rotate ball bearingscrew 116. The rotation of screw I16 causes screw nut 102 to be movedalong the groove of the screw I16 to cause spring I18 to drive piston 96to the right as viewed in FIG. 4. Movement of piston 96 to the rightcauses the fluid in chamber 84 to be forced therefrom, through line 74and into the fluid compartment of actuator 38. The fluid entering fluidcompartment 76 in actuator 38 causes piston 58 to be moved to the left,as viewed in FIG. 3, which causes push rod 42 to be extended from theactuator 38 which in turn causes support 26, and hence the patientsfingers, to be moved towards the thumb support 24.

The numerals I12, I14 and 116 refer to the skin electrodes which areplaced adjacent the skin surface of the patients arm as indicated inFIG. I and maintained thereon by suitable means such as tape or thelike. The electrodes are connected to a muscle potential amplifiergenerally referred to by the reference numeral 118 in FIGS. 5 and 6. Ifthe patient desires to close his fingers, he tenses a muscle locatednear the skin surface electrodes. The resulting muscle potentials arethen amplified by the muscle potential amplifier 118. This amplifierFIG. 6, consists ofa pair of operational amplifiers in a unity gain tocommon mode type circuit followed by a differential amplifier circuit, aparallel T" rejection filter circuit, and a Darlington amplifiercircuit. The amplified myopotentials are then put into a detectorcircuit 120, consisting of a Schmidt trigger circuit followed by alow-pass filter circuit. This detector circuit transforms the amplifiedmuscle potentials into a slowly varying control signal whose amplitudeis related to the muscle tension causing it. if the output of thedifferential amplificr T24 is sufficiently large the motor controlcircuit 126 causes the motor 106 to drive the hydraulic pump 78 until apressure related to the desired finger position plus tension is reached.The motor control circuit contains two identical control circuitsconsisting of a relaxation oscillator circuit which drives a hybridtiming circuit and a transistor bridge circuit. In this way bothclockwise and counterclockwise rotation can be obtained depending uponwhich control circuit drives the transistor bridge circuit. The motor W6stops when the signal from the pressure transducer 86 causes thedifferential amplifier B24 output signal to go below a set thresholdlevel. If the patient wishes to open his fingers, he simply relaxes andthe signal from the pressure transducer 86 causes the motor 106 toreduce the pressure so that the brace is driven to its zero musclevoltage position by the spring 68 contained in the actuator 33.

In summary, it can be seen that the myoelectric brace is driven bymuscle potentials. The muscle potentials are created by tensing orcontracting of the muscle which causes polarization of the muscle. Theelectrodes on the skin detect the E.M.G. differential and relays thesame to the circuitry illustratcd in the drawings. The pump 78 andactuator 38 are especially designed to reduce friction through the useof the ball bushings 64 and 66 and through the use of the foldablebellowfram incorporated therein.

A brace has been provided which is lightweight and which requires aminimum of power to be consumed during the operation thereof. The sizeof the brace is relatively small and is conveniently secured to thepatients arm. Finger position and lietlSlOtt is controlled in aproportional manner due to the muscle potentials being sensed by thesurface electrodes and the relationship of the pressure transducer tothe motor control circuit,

Thus it can be seen that the device accomplishes at least all ofitsstated objectivesv lclaim:

l. in a myoelectric brace, comprising,

a splint means adapted to be secured to a person's arm and having afixed wrist-hand splint portion and a movable finger support meanspivotally connected thereto,

a hydraulic actuator means mounted on said fixed wristband splintportion and being connected to said movable finger support means tocause said finger support means to be moved with respect to said fixedsplint portion,

a hydraulic pump means fluidly connected to said actuator means adaptedto cause said actuator means to move said finger support means,

a motor means for operating said pump means,

an electrode means adapted to be placed on the wearer's skin surfaceadjacent a muscle capable of being tensed by the wearer,

a circuit means connected to said electrode means adapted to sense themyopotentials created by the tensing of said muscle and to transform thepotentials into a control signal whereby said electric motor, said pumpand said actuator will be operated so that said finger support meanswill be moved towards said fixed splint means, and

said pump means including a hollow piston head housing having a fluidcompartment provided therein, said fluid compartment being in fluidcommunication with said actuator means, a cylinder housing connected tosaid piston head housing, a bellowfram between said piston head housingand said cylinder housing, a piston means in said cylinder housingconnected to said bellowfram for movement therewith, a ball bearingscrew rotatably mounted in said cylinder housing, a screw nutoperatively connected to said piston means in engagement with said screwwhereby rotation of said screw will cause said piston and saidbellowfram to be moved, said motor having a drive shaft connected tosaid screw. I 2. The brace of claim 1 wherein a pressure transducer isin communication with said fluid compartment in said piston headhousing, said pressure transducer being electrically connected to saidcircuit means to stop said motor when a predetermined pressure isreached in said fluid compartment.

1. In a myoelectric brace, comprising, a splint means adapted to besecured to a person''s arm and having a fixed wrist-hand splint portionand a movable finger support means pivotally connected thereto, ahydraulic actuator means mounted on said fixed wrist-hand splint portionand being connected to said movable finger support means to cause saidfinger support means to be moved with respect to said fixed splintportion, a hydraulic pump means fluidly connected to said actuator meansadapted to cause said actuator means to move said finger support means,a motor means for operating said pump means, an electrode means adaptedto be placed on the wearer''s skin surface adjacent a muscle capable ofbeing tensed by the wearer, a circuit means connected to said electrodemeans adapted to sense the myo-potentials created by the tensing of saidmuscle and to transform the potentials into a control signal wherebysaid electric motor, said pump and said actuator will be operated sothat said finger support means will be moved towards said fixed splintmeans, and said pump means including a hollow piston head housing havinga fluid compartment provided therein, said fluid compartment being influid communication with said actuator means, a cylinder housingconnected to said piston head housing, a bellowfram between said pistonhead housing and said cylinder housing, a piston means in said cylinderhousing connected to said bellowfram for movement therewith, a ballbearing screw rotatably mounted in said cylinder housing, a screw nutoperatively connected to said piston means in engagement with said screwwhereby rotation of said screw will cause said piston and saidbellowfram to be moved, said motor having a drive shaft connected tosaid screw.
 2. The brace of claim 1 wherein a pressure transducer is incommunication with said fluid compartment in said piston head housing,said pressure transducer being electrically connected to said circuitmeans to stop said motor when a predetermined pressure is reached insaid fluid compartment.